(R)-2-(4-Chloro-1H-pyrazol-1-yl)propanoic acid (105 mg, 0.60 mmol) and (R)-tert-butyl 2-amino-6-(3-(pyrrolidine-1-carbonyl)piperidin-1-yl)pyridin-3-ylcarbamate (195 mg, 0.50 mmol) were dissolved in ethyl acetate (0.5 mL) with pyridine (0.20 mL, 2.5 mmol) at room temperature. The mixture was cooled to 0° C. 1-Propanephosphonic acid cyclic anhydride (0.375 mL, 50% solution in ethyl acetate, 1.25 mmol) was added while stirring at 0° C. The resulting mixture was stirred for 15 min, and then warmed to room temperature. After stirring for 1.5 h at room temperature, the mixture was quenched with an aqueous solution of hydrochloric acid (0.5 M, 1 mL). The mixture was partitioned between ethyl acetate (10 mL) and water (5 mL). The organic layer was washed sequentially with water (5 mL), a saturated aqueous solution of sodium bicarbonate (5 mL), and brine (5 mL). The organics were dried over magnesium sulfate, filtered, and concentrated. The residue was dried under reduced pressure to afford tert-butyl 2-((R)-2-(4-chloro-1H-pyrazol-1-yl)propanamido)-6-((R)-3-(pyrrolidine-1-carbonyl)piperidin-1-yl)pyridin-3-ylcarbamate (268 mg, 98% yield). 1H NMR (500 MHz, CDCl3) δ 1.48 (s, 9H), 1.48-1.55 (m, 1H), 1.73-1.76 (m, 1H), 1.80-2.05 (m, 6H), 1.86 (d, 3H), 2.53-2.59 (m, 1H), 2.84-2.90 (m, 1H), 2.96-3.01 (m, 1H), 3.43-3.51 (m, 3H), 3.55-3.60 (m, 1H), 4.12 (br d, 1H), 4.33 (br d, 1H), 5.10 (br s, 1H), 6.56 (d, 1H), 7.30 (br s, 1H), 7.57 (s, 1H), 7.61 (s, 1H), 7.76 (br s, 1H), 8.58 (br s, 1H); MS (ES+) (M+H) 546.3; Chiral HPLC retention time 4.61 min (Method: Chiralpak AS-H 0.46×25 cm; Mobile Phase: CO2/methanol; Flow: 2.5 mL/min); 97.1% de.
